Field of the Invention
This invention deals with non-impact type printers. More specifically, it deals with a non-impact type printer, such as a thermal printer having a printhead that is wide enough to record a plurality of characters. The relatively wide printhead must be pressed against a printing medium which is driven by a print roller. To achieve uniform print density and clarity, it is important that the pressure across the entire printhead be substantially the same.
In the prior art, non-impact type printheads have been moved across the print medium to form characters in a step-by-step fashion. The printhead required for this type of printer is generally quite small and therefore application of even pressure is a relatively simple matter. However, as the printhead is made wider, slight variations in the print roller and in the print medium may cause the printhead to fully contact one portion of the print medium and barely touch other portions.
To overcome this problem, prior art techniques have involved the very careful machining of the print roller to insure surface uniformity. This technique involves high machining costs and also requires springloaded pinch roller devices bearing against the print medium, which in turn bears against the print roller to move the print medium.
This invention permits the manufacture of a relatively cheap, resilient print roller in combination with a printhead tht is capable of pivoting around at least two axes. The resiliency of the print roller material also enables the use of stationary pinch rollers whose grasping action of the print medium is afforded by the resiliency of the roller itself, reducing the need for spring-loaded pinch rollers.